Remote desktop type software that the client need not install anything [closed]

You want Single-Click VNC

http://www.uvnc.com/addons/singleclick.html

1. It's an EXE they can toss at the end
2. If you have a VNC server that supports reverse VNC, you are good to go
3. Yes
4. You modify your router settings, they only need outbound 5500 TCP

Take a look at TeamViewer.

• The Quick Support is a single executable that establishes a connection.
• Works on Windows and Mac OS X.
• Free for personal use, one-time payment for business use.
• Has other features other solutions don't have, like creating a VPN between you and your client as well as being able to flip the viewer/presenter roles for doing presentations or demonstrations.

My vote would go towards LogMeIn Rescue.

1. No software to install
2. Works on a Mac
3. Not free
4. No need to mess with any settings.